Hydraulic apparatus for pulsating the diaphragms of pulp mill screens



Oct. 10, 1950 F. DUSTAN mawuc APPARATUS FOR PULSATING 1141-:

DIAPHRAGMS 0F PULP MILL SCREENS Filed July 11, 1945 5 Sheets-Sheet l Ilxlr'lillilllln'lll 3 Sheets-Sheet 2 QM bk F. DUSTAN HYDRAULIC APPARATUSFOR PULSATING THE DIAPHRAGMS OF PULP HILL SCREENS Oct. 10, 1950 FiledJuly 11, 1945 Oct. 10, 1950 F. DUSTAN HYDRAULIC APPARATUS FOR PULSATINGTHE DIAPHRAGMS OF PULP MILL SCREENS 3 Sheets-Sheet 3 Filed July 11, 19456 4 240 6 w wmmmmmmwww w ,r f r S 4 w 0 I F H r @6 A; w filo 4 U B BBQW2U 6 2w2b. Mm 24 2 Q B O/ QM 44 4 4 4 111!) i\ A 3 v. ll M Il-lI- 8 w 8& E B B 3 I van to! Prams 10,1950 f HYDRAULIC APPARATUS FOR PULSAT- INGTHE DIAPHRAGMS F PULP MILL SCREENS Frank Dustan, Fitcliburg, Mara,

anignor to National Lead Company, New York, N. Y., a corporation of NewJersey Application July 11, 1945, Serial No. 804.31!

The present invention relates to hydraulic pulsating apparatus, and moreparticularly to improvements in apparatus for pulsating the diaphragmsof flat pulp mill and paper mill screens.

In the usual arrangements, the diaphragms are vibrated by directmechanical connections from cranks or eccentrics to provide rapidlyalternating pressure and suction strokes in the diaphragm chamber. Theforces involved are large, so that the moving parts must be stronglyconstructed and firmly supported. Because of the positive nature of thedrive, there is likelihood of serious damage if the screens becomeclogged or if the diaphragm chamber becomes flooded. I

In my prior Patent No. 2,368,291, issued January 30, 1945, there isdisclosed apparatus which overcomes many of the difliculties inherent inconventional pulsating apparatus.- In place of positive mechanicalactuation, hydraulically operating mechanisms are provided, withindividual hydraulic power drives for each diaphragm. These-drivesinvolve power pistons and cylinders, to which hydraulic fluid underpressure is admitted under the control of individual control valvesadjacent-each power cylinder. The control valves are actuated at highspeed byv mechanical means to cause fluid under pressure to be suppliedalternately to one side and then the other of the power pistons. Thesehydraulically operating drives, in conjunction with pressure reliefmeans for limiting the maximum value of fluid pressure that may beapplied, provide normal diaphragm pulsation under favorable screeningconditions, but permit the diaphragm stroke to be reduced automaticallyif excessive screen resistance develops, and thereby prevent damage tothe machine.

In this prior arrangement there is an appreciable loss in efliciencybecause of the rapid reversals in flow which must occur in the pipingbetween control valve and power cylinder in order to pulsate thediaphragms at the high frequencies generally employed. Not only is therean appreciable resilience in the piping, but it is difficult to provideand maintain tight connections under the prevailing conditions of highfluid pressure and severe vibration.-

To suit various grades of stock, the diaphragm stroke must be capable ofvariation. In my prior arrangement, the adjustment for stroke length isprovided by means of spacing collars of various thickness which functionin conjunction with fixed abutments to provide positive limits to themovement of the power piston. By changing these spacing collars orshims, the

1 Claim. (Cl. sa-sz) diaphragm stroke may be varied to meet differentscreening conditions. 1

The present invention is concerned with improvements in hydraulicallyoperating pulsating apparatus of the general type disclosed in my priorpatent, whereby to increase the effectiveness of operation. One of theobjects is to provide mechanism which permits the stroke adjustment tobe made in a simple and precise manner without the use of shims, collarsor other positive limit stops.

Another object of the invention is to provide hydraulic pulsatingapparatus in which the power cylinder and the control valve are combinedin a single compact unit so as to eliminate intervening connecting pipesand thereby afiord very short paths for the flow of hydraulic fluidbetween control valve and power cylinder.

It is likewise an' object of the invention to provide an improvedhydraulic power amplifying mechanism of compact and eificientarrangement, capable of providing a power stroke or movement thatreproduces rapidly and accurate- 1y a'stroke or displacement takingplace at a relatively low energy level.

In the drawings illustrating the invention in its preferred form, Fig. 1is a view in side elevation of a portion of a pulp mill screen, showingthe driving mechanisms for two diaphragms thereof; Fig. 2 is a sectionalelevation'of the machine, taken on the line 2-2 of Fig. 1; Fig. 3 is adetail sectional elevation of an hydraulic pulsating unit; Fig. 4 is asectional detail of the power piston thereof, turned about its axis fromthe position shown in Fig. 3; and Fig 5 is an end view of the powerpiston shown in Fig. 4.

The screen shown in Figs. 1 and 2 is, in its general features, ofconventional construction and arrangement. A vat 6, into which the stockis introduced, is provided with flat screen plates 8 which arepreferably of the type shown in my Reissue Patent No. 20,533, dated Oct.19, 1937. Mounted below each pair of plates is a rubber diaphragm l0,secured at its edges to the vat frame l2. The space between the platesand the diaphragm constitutes the diaphragm chamber l6.

Connection to the central portion of the diaphragm is made by means of aframe 20 to which the diaphragm is clamped. The frame is secured to theupper end of a guide member 22 which slides within a cylindricalguideway 24 in cross member 26.

To reciprocate the diaphragms, the guide members 22 are connected tohydraulic power drive units 30 which are mounted on the cross members 26directly below the guides. These power units embody within a singlecasing the controlling as well as the driving elements ofan hydraulicsystem, so as to provide a compact arrangement having extremely shortflow paths for the hydraulic fluid.

' Theunits comprise a power cylinder 32 within which is a power piston34 having a drive rod 35 for connection to the guide 22. Movement of thepower piston is under the control of a piston valve 38 which operateswithin the power piston, the latter thus serving as a cylinder for thepiston valve in addition to its function as power piston. The cylinder32 is closed at its ends by heads 42 having stufllng boxes 44 to providea seal for the drive rod 36 and piston valve rod 46.

To actuate thehydraulic driving unit, fluid under pressure is suppliedfrom a motor-driven hydraulic pump indicated generally at 48 and similarto that shown in my Patent No. 2,368,291.

.The fluid is distributed by a line of piping 50 to the inlet port 52 ofeach cylinder, and is discharged through exhaust port 54 to a'returnline 56 running to the pump. A relief valve 58 maintains substantiallyconstant fluid pressure in the supply line 50, returning excess fluidthrough a by-pass 60 directly to the pump.

The hydraulic driving units operate to pulsate the diaphragms at astroke and frequency determined by the stroke and frequency imparted tothe piston valves. To reciprocate the piston valves, each driving unithas associated therewith an eccentric drive assembly I mounted on ashaft I2 and connected to the piston valve rod 46 by a link I4. Eachshaft is independently journalled in the lower ends of arms I6 dependingfrom the driving unit 30. Couplings I8 connect the several shafts, whichare driven by a variable speed drive 80 of conventional construction.Adjustment for stroke length is provided by means of a conventionaltwo-part eccentric disc 82, the outer portion of which may be locked inany one of several positions relative to the inner member to vary thethrow or stroke.

The arrangement of power piston and piston valve, by which the former iscaused to reproduce at a high power level the movement of the latter,will now be described. The piston valve is provided with three lands 90,92 and 94, these lands 0 being separated by piston sections of reduceddiameter. The upper end 01' the piston valve slides in a blind passage96 in the :power piston, and the piston valve rod emerges from the powerpiston through a bore 88.

Within the body of the power piston are four internal lands, I00, I02,I04 and I06, which, in cooperation with the piston valve, define fivespaced annular regions H0, H2, H4, H6, and H8. The central region II4receives hydraulic fluid under pressure through a port 20 whichcommunicates with inlet port 52 over the normal range of movement of thepower piston. Communication between region H2 and the cylinder chamberI22 below the power piston is provided by a pair of oppositely disposedports I24 which open into downwardly directed channels I26 along thepiston wall. In similar fashion region IIIi communicates with the uppercylinder chamber I28 by way of ports I30 and channels I32. The endregions H0 and H8 are provided with ports I34 and I36 which open into acommon channel I38 communicating with exhaust port 54 in the cylinderwall.

The power piston thus cooperates with the piston valve to provide a fourway valve for controlling fluid admission and discharge to the powercylinder. By reason of this identity of the power piston with thecylinder for th piston valve, the follow-up relationship that ischaracteristic of a servomechanism is inherently provided.-

The mode of operation by which the power piston is caused to reproducewith. great accuracy a movement or displacement of the piston valve mayreadily be traced. Starting with the parts as shown in Fig. 3, with thepower piston and piston valve at their mid-positions, assume that aclockwise rotation of shaft 12 takes place, thereby raising the pistonvalve. This permits fluid to flow from central region I I4 past pilotpiston land 92 into the region I I2 and thence to the cylinder chamberI22 below the power piston. A relatively short and rigidly definedpassage is provided for the supply of fluid under pressure from theinlet 52 to the working chamber I22. The opposed Y ports I24 andchannels I26 aid in balancing the fl-uid pressures acting laterally onthe power piston.

At the same time that the piston valve is admitting fluid to theunderside of the power piston. communication is provided between theexhaust port 54 and-the upper chamber I28 to permit the discharge ofhydraulic fluid therefrom. The flow path is by way of channels I 32 intoannular region II6, thence past land 84 into region H8 and through portI36 to the discharge channel From this upward movement of the pistonvalve there consequently results an upward movement of the power piston.This movement reaches a limit determined by the new position of thepiston valve, since the admission of fluid terminates when land 92 ofthe piston valve becomes centered between lands I02 and I04 of the powerpiston.

Because of the short flow paths and the rigid nature of the passages,the power piston is able to follow accurately the movements of thepiston valve even though these movements take place with great rapidity.Reciprocation at a frequency of several hundred cycles per minute mayreadily be followed, with the stroke of the diaphragm determined by thelength of stroke imparted to the piston valve as determined by thesetting of the adjustable eccentric 82.

As disclosed in my prior patent, it is desirable that the pulsations ofthe several diaphragms take place in staggered sequence rather than insynchronism, so as to minimize vibration in the machine as a whole.Furthermore, the stroke length should be correlated with pulsationfrequency to suit the particular stock. As pointed out in that patent,it is generally suitable to have the stroke and frequency inverselyproportional, in which event the consumption of hydraulic fluid by thepower units remains substantially constant. By setting the by-passrelief valve to maintain a pressure adequate for normal diaphragmpulsation, proper operation over the usual range of adjustments ofstroke and frequency is provided. In the event unfavorable screeningconditions develop, involving reduced diaphragm amplitude or a completestoppage, the by-pass valve serves to limit the forces developed by thedriving unit and thereby prevent damage or destruction to the mechanismsassociated with the involved section.

While the hydraulic driving unit has been described in association withmechanism for pulsating pulp mill and paper mill screens; it is notlimited to such embodiment, but may be employed effectively in otherapplications where an hydraulic servomechanism is required that iscapable of accurate and eflicient operation at high frequencies andwhere a compact coaxial arrangement of the control and power outputelements is advantageous.

I claim:

Hydraulic pulsating apparatus for pulsating the diaphragms of fiat papermill and pulp mill screens comprising a power cylinder, a power pistonreciprocable within the cylinder, apiston rod connected to thediaphragm, a piston valve within the power piston, the piston valvehaving lands and passages cooperating with the power piston to form afour-way control valve for causing the power piston substantially toreproduce the movement of the piston valve, means for supplyinghydraulic fluid under pressure to the control valve, a rotating driveshaft, an eccentric on the drive shaft having relatively adjustableparts to provide adjustment of eccentric stroke, and connections betweenthe eccentric and the piston valve for positively reciprocating thepiston valve in accordance with the stroke of the eccentric.

FRANK DUSTAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

